Chapter 5 - Section 5.7 - Negative Exponents and Scientific Notation - Exercise Set - Page 409: 48

$\dfrac{1}{y^{11}}$

Using the laws of exponents, the given expression, $ \dfrac{y^{-5}}{(y^3)^2} ,$ simplifies to \begin{array}{l}\require{cancel} \dfrac{y^{-5}}{y^{3(2)}} \\\\= \dfrac{y^{-5}}{y^{6}} \\\\= y^{-5-6} \\\\= y^{-11} \\\\= \dfrac{1}{y^{11}} .\end{array}